Seal for a pothead hoodnut



Sept. 26, 1967 R. A. PHlLrBERT ETAL 3,344,223

SEAL FOR A POTHEAD HOODNT Filed Jan. v, `196e FIG. I 4Pvior APT FlG. 2Pridr Art fai ` INVENTOR. R. A. PHILIBE-RT, F. L 'BRowNE BY AND R.F;.POLIMINE THEIR ATTORNEY United States Patent O 3,344,223 SEAL FOR APOTHEAD HOODNUT Robert A. Philibert, Rockville Centre, Frank L. Browne,Wantagh, and Robert F. Polimine, Brooklyn, N.Y., assignors to @.Z.Electrical Manufacturing Co., Inc.,

Brooklyn, N.Y., a corporation of New York Filed Jan. 7, 1966, Ser. No.519,330

1 Claim. (Cl. 174-19) This invention relates to potheads, and moreparticularly pertains to a seal for a removable hoodnut for the pothead.

It has been found that the use of potheads having removable hoodnutshave often developed leakage and that the insulation of the cablesterminated in the pothead has become deteriorated.

An investigation into this matter discloses that the formation of airpockets during the insertion of the compound into the pothead leavesspaces which may cause trouble. In particular, since the pothead isiilled with insulating compound while it is heated, the cooling of thecompound causes it to contract and in effect create air pockets with alower pressure than the ambient air pressure which has a tendency tosuck in air from the outside and moisture along with it under certainconditions. Also, when a considerable amount of current is being carriedby the conductor terminating in the pothead, the pothead becomes heated.This causes the air in the spaces not iilled with compound to developpressures tending to cause such air to nd leaks for escaping. If thepothead hoodnut seal is not perfect, air will ow out of the pothead andupon the reduction of the current load, when the pothead cools, a vacuumwill develop which will draw air with moisture into the pothead.

The moisture alone within the pothead will cause the cable insulation tolose its dielectric properties, particularly when paper insulated leadcable is employed. It is also known that corona discharges cause aformation of ozone, and ozone is known to cause the erosion of cableinsulation. Also, corona develops at lower potential values whenmoisture is present. Thus, it is of utmost importance that air 'withmoisture contained therein be excluded from the pothead. Basically, apothead is a hermetic seal to keep air and moisture away from theinternal stress cone termination for the cable.

The purpose of the present invention is to provide an improved sealbetween the hoodnut (or capnut) and the body portion of the potheadinsulator.

It is the purpose of the present invention to not only increase thepressure which the seal will withstand without leakage, but also to soconstruct the seal that it will maintain its eitectiveness over a periodof time without deterioration.

Other objects, purposes and characteristic features of the presentinvention will be in part obvious trom the accompanying drawings, and inpart pointed out as the description of the inventionl progresses.

In describing the invention in detail, reference will be made to theaccompanying drawing, in which like reference characters designatecorresponding parts throughout the several views, in which- FIG. lillustrates a vented hoodnut with the usual at seal between the hoodnutand the insulator such as might be used in DAscoli et al. Patent No.3,151,209, granted Sept. 29, 1964, without the hoodnut being tighteneddown;

FIG. 2 illustrates the hoodnut of FIG. 1 as being fully tightened andshowing the deformation of the rubber seal;

FIG. 3 illustrates a hoodnut constructed in accordance with the presentinvention but not yet tightened down;

FIG. 4 illustrates the hoodnut of the present inven- ICC tion fullytightened with the disposition of the seal being determined by thenature of the hoodnut embodying the present invention; and

FIG. 5 is a partial sectional view ofva hoodnut to show the shape of thegroove placed therein (enlarged) and shown in FIGS. 3 and 4.

In referring to FIG. 1 of the DAs-coli et al. Patent No. 3,151,209, itwill be noted that the space between the stem 26 and the insulator 14 isrelatively small. It was thought that such a small spacing might preventthe adequate lio'w of the hot insulating compound even though the airmight be vented through an appropriate vent. Therefore, the structurewas modified to include adequate spacing for the compound to flow; ascrew closed vent 29 was added to the hoodnut; and a hat gasket orwasher 27 was inserted between the hoodnut 28 and the insulator 14, asshown in FIG. l of the drawings herein with hoodnut untightened. Suchstructure, with the hoodnut 28 tightened and the insulating compoundinserted in the pothead in the usual way still had the same problems.Further investigation showed that the seal 27 spread or deformed undulyunder the pressure of the tightened hoodnut 28 as shown in FIG. 2herein. The seal 27 spread suiciently to actually prevent the adequateventing of the air within the pothead during the insertion of the hotinsulating compound.

Referring to FIG. 3, the insulator body portion 5 of the pothead of thepresent invention is so constructed internally near its upper end as toinclude winged portions 6 which cooperate with winged portions 7 on thestem 8 to prevent the turning of the stem 8 although allowingconsiderable free space for the passage of insulating compound into theair spaces above it. The particular formation of the insulator portion 5is not limited to this particular form, but it should be provided withadequate structure for holding the stem 8 from turning and at the sametime provide adequate passages for the flow of the insulating compoundand venting of air from the threaded vent hole 9 during itsconstruction.

The lower portion of the insulator body 5 has not been shown in thedrawings, but it is assumed to be connected to a suitable metal bell(not shown) adapted to receive a cable through a suitable seal. It isalso assumed that the metal bell has a threaded opening for a connectionto a source of dielectric material -or compound. This threaded openingalso would have a threaded closing plug. This structure may be of anysuitable type, and one such suitable form is shown, for example, in theabove mentioned Patent No. 3,151,209. Also, the compound filling for thepothead can be any suitable dielectric material, or it can be thecompound disclosed in such patent.

The capnut or hoodnut 10 is adapted to screw onto the threaded portionof the stem 8 after the ilat sealing ring 11 is placed into position.This is shown in FIG. 3 where the` hoodnut 10 has been just tightenedsuiciently to Contact the sealing ring 11.

It will be noted that the hoodnut or capnut 10 has a circular groove 12included therein which has been illustrated in an enlarged sectionalview in FIG. 5. In one embodiment of the invention this groove was inthe order of 1a-inch diameter with 1%.,2 round corners. In thisembodiment a sealing ring of neoprene rubber 1r-inch thick was used.Neoprene was selected because it is `basically a high Durometer rubberwith low compressive set, wide temperature range and good tensilestrength. It also resists erosion by ozone. Su-ch sealing rings can bepurchased from various suppliers; but any other suitable sealing ring ofcompressive material can also be used, if desired, such as nitrile (BunaN) articial rubber.

Upon tightening the hoodnut 10 of this one embodiment of the inventionto two hundred inch pounds torque, there was no blocking of thepassageway by the sealing ring 11 since it assumed the general shapeshown in FIG. 4. There was no leakage from the gasketed vent screw 13and there was no leakage around the seal 11 at one hundred twenty poundsper square inch internal air pressure.

In fact, tightening of the hoodnut to seven hundred inch-pounds torquedid not cause the sealing ring 11 to expand unduly, but it still alloweda free passageway for the venting air and for receiving the insulatingcornpound. When the unit was disassembled, the sealing ring 11 was notscraped or cut in any way.

On the other hand, the tightening of the hoodnut 23 of FIG. 2 toapproximately 700 inch-pounds torque caused slight cutting or abrasionof the sealing ring 27 besides causing it to protrude and block the venthole 29 as shown in FIG. 2. In fact, the tightening of the hoodnut 28lof FIG. 2 to approximately 25() inch-pounds torque caused the sealingring to expand and block the flow of air from the vent hole 29, althoughsuch pressure did not cut the sealing ring.

Before inserting the ring 11, it was suitably covered with a speciallubricating grease compatible with rubber.

The grooved portion 12 of the hoodnut 10 and the at portion 15 of theinsulator 5 was also greased. The application of the pressure due to thetightening of the hoodnut to the standard two hundred inch-pounds torquewith a suitable wrench appeared to cause the rubber to actually flowinto the groove 12 without causing the inner and outer periphery of thering 11 to unduly extend. The grease allows any air in the groove 12 toreadily escape as the hoodnut 10 is tightened.

One theory of the function of the groove in the hoodnut is that thepressure per unit area is increased around the inner and outer edges `ofthe surface 15 so as to cause the seal 11 to tightly embed the roughnessof the unglazed (and unfinished) portion of the insulator 5, and at thesame time allowing the groove to receive and in fact draw into it aportion of the sealing ring 11 to which pressure is also applied by thehoodnut 10. In this connection, it is to be understood that the surface15 along the upper edge of the insulator 5 is slightly rough and in thesame condition as when it was rough ground. If this surface is nelyfinished or polished, then the sealing effect in FIG. 2 would beimproved, but the ring 27 would still be deformed blocking the venthole. However, the use of the groove 12 both improves the sealing effectand prevents undue deformity of the ring 11. It is also noted that theincreased cross section of rubber at the groove 12 also tends tomaintain resiliency over long periods of time.

Another theory of operation is that the groove collects the rubber andconcentrates the pressures directly under it onto the surface 15 tocause any unevenness to more readily be embedded and form a tighterseal.

Regardless of the particular theory of the functioning of the groove,the practical results obtained are a highly satisfactory sealparticularly useful for a pothead, although other uses may be found towhich the seal may be put.

It is also to be understood that a pothead using this seal isconstructed in the usual way by the insertion of hot insulating compoundinto the lower metal bell of the pothead (not shown) with the vent screw13 removed. As this compound rises in the metal bell and insulatorsection of the pothead, it ultimately begins to flow out of the vent 9,at which time the screw 13 with its O-ring gasket of neoprene rubber isplaced is inserted into the vent 9 and the pothead gradually cooled.When the insulating compound has solidified, the source of the cornpoundis removed and a closing plug is inserted into the connecting hole.

Having thus described one form of seal for a pothead hoodnut as onespecific embodiment of the present invention, it is desired to beunderstood that this form is selected to facilitate in the disclosure ofthe invention rather than to limit the number of forms which it mayassume; and, it is to be further understood that Various modifications,adaptations and alterations may be applied to the specific form shown tomeet the requirements of practice without in any manner departing fromthe scope of the present invention.

What is claimed is:

In a pothead structure, an insulator body being hollow for allowing thesealed entrance of a cable at its lower end and having a flat circularsurface at its upper end, a metal stern extending out of said insulatorat its upper end and connected to said cable at its lower end, saidupper end of said stem being threaded and said lower end of said stemcontacting said body of said insulator to prevent rotation of said sternrelative thereto but providing the free passage of air and any uiddielectric material inserted into said insulator body, a at gasket ofresilient rubber material located on said dat circular surface at theupper end of said insulator body, and a capnut threaded onto said stemagainst said at gasket, said capnut having a closable vent, and alsohaving a generally flat and now-confining circular surface matching theflat circular surface of said insulator body but having therein anannular groove centrally located radially in said flat surface relativeto the at surface of said insulator body, said annular groove having across-sectional area for receiving substantially all of the resilientrubber material of the gasket displaced from its normal position by thetightening of the capnut onto said stem.

References Cited UNITED STATES PATENTS 2,049,749 8/1936 Roth 174-752,117,697 5/1938 Brandt 174-12 X 2,284,926 6/1942 Smith l74-l672,289,l64 7/1942 Arnold et al. 174-163 X 2,300,858 11/1942 Arnold et al.174-167 X 2,476,074 7/1949 Unger 174-152 2,719,875 l0/l955 Cronin174-152 X 3,151,209 9/1964 DAscoli et al. l74-l9` OTHER REFERENCESElectrical Wire and Cables, catalog 37, published by General CableCorporation, 1938, pp. 5 and 19 of section 17.

LARAMIE E. ASKIN, Primary Examiner.

